As usual with browser bugs and hacks this took me a while to find out.
I have an unordered list with complex items like floats and stuff. This list is supposed to hide when I click on a button by slowly decreasing its height. I use jQuery's slideToggle for that.
Problem: In Internet Explorer 6 the content (or parts of it) is hidden after the list is shown (slid down).
The only thing I found was a blog post saying you shouldn't use any positioning there.